(a) Field of the Invention
The present invention relates to an electronic musical instrument, and more particularly it pertains to a waveshape memory type electronic musical instrument which is provided with memory means for storing and reproducing the waveshape of tone signals.
(B) Description of the Prior Art
In a waveshape memory type electronic musical instrument, a standard waveshape of a musical tone signal is preliminarily stored in a memory means and is read out upon each key depression at a speed corresponding to the pitch of the tone of the depressed key. An example of the waveshape memory type electronic musical instrument is shown in FIG. 1. When a key in a keyboard 10 is depressed, a reference number memory (referred to as R number memory, hereinafter) 11 is activated to generate an R number signal therefrom and a key-on signal KON is generated from the keyboard 10. The R number is related with the pitch of the depressed key and is proportional to the fundamental frequency of the tone to be sounded. The R number read out from the memory 11 is supplied to a cumulative adder 13 through a gate 12 which is opened by a clock pulse .phi. of a predetermined period. The adder 13 carries out the cumulative addition of the R number supplied from the memory 11 through the gate 12 which is opened at the timing of the clock pulse .phi.. Thus, the adder 13 supplies the temporary sum to a waveshape memory 14 as its address signal. Namely, the adder 13 delivers R (number below radix point, in general) at the timing of the first pulse .phi., 2R at the timing of the second pulse .phi., and similarly qR at the timing of the q-th pulse .phi. to call the address of the respective waveshape samples in the waveshape memory 14. Here, the adder 13 contains integer digits and fraction (below radix point) digits and has a modulus of a predetermined number, e.g. 128. Thus, the cumulative sum x = .SIGMA.R = qR increases from "0" to the modulus with a pitch of R. When the sum qR exceeds the modulus, the difference between the sum and the modulus remains in the adder 13. Then, similar cumulative addition is performed thereon. Since the R number is proportional to th fundamental frequency of the musical tone to be sounded, the increasing rate of the sum x = qR and hence the repetition frequency of the stepping-up in the adder, f = R.multidot..nu./128, becomes also proportional to the fundamental frequency of the musical tone to be sounded, wherein .nu. represents the repetition frequency of the clock pulse .phi.. When the number of memory samples or stages in the waveshape memory 14 is equal to the modulus of the adder 13, the frequency of the waveshape produced from the waveshape memory 14 becomes equal to the aforementioned frequency f and is porportional to the magnitude of the R number. It will be seen that the repetition frequency f of the waveshape production represents the fundamental frequency of the musical tone to be sounded. That is, when a large R number is generated, the output of the waveshape memory 14 varies rapidly, and the period of one waveshape production becomes short and a musical tone of a high fundamental frequency f = R.multidot..nu./128 is generated. On the contrary, when a small R number is generated, a musical tone of a low fundamental frequency is generated. The details of the structures and operations of such functional units are disclosed in Japanese Patent Laid-open Publication No. 48-90217 (corresponding to U.S. Pat. No. 3,809,786 to Ralph Deutsch issued on May 7, 1974).
The waveshape memory 14 stores the sample values of the waveshape of the musical tone in digital representation. Since the repetition frequency of the waveshape production is varied to be equal to the fundamental frequency of the musical tone to be sounded, the output of the waveshape memory 14 carries both the waveshape (i.e. tone color) information and the tone pitch information. Such a digital output signal of the waveshape memory 14 is multiplied by an envelope signal supplied from an envelope generator 15 in a multiplier 16. The digital tone signal now afforded with an envelope is converted into a corresponding analog signal in a digital-to-analog (D/A) converter 17. This analog signal is sounded as a musical tone from a loudspeaker 19 through an audio device 18 including an amplifier, etc.
The envelope generator 15 is activated by the key-on signal KON as shown in FIG. 2A generated by the depression of a key in the keyboard 10, and generates an envelope signal ENV as shown in FIG. 2B. The envelope signal ENV is formed of three portions; attack ENV.sub.1, first decay to sustain ENV.sub.2 and second decay ENV.sub.3. The tone signal from the waveshape memory 14 is multiplied by such envelope to form an expression-rich musical tone signal. That is, the envelope of FIG. 2B shows how the musical sound grows to the maximum amplitude upon depression of a key (attack), then attenuates to a sustain level (first decay) and keeps the nearly constant level (sustain), and finally upon release of the key gradually attenuates and vanishes (second decay).
According to such a waveshape memory type electronic musical instrument, the amplitude of a tone is varied according to the envelope function generated from the envelope generator but the tone color is kept constant from the attack to the decay since the waveshape memory stores a predetermined waveshape and produces the same waveshape repeatedly. Such a constant color sound is far different from the rich sound of a natural musical instrument which changes the tone color delicately from the attack to the decay.